Unit 5 Review
DNA, Protein Synthesis, Mutations
Griffith
• Bacterial Transformation
Hershey and Chase
• DNA is the hereditary material
Watson, Crick, Franklin
• Franklin: X-Ray crystallography
• Image of DNA
• Watson and Crick: Built the 3D Model of DNA
Chargaff
A-T
C-G
Nucleic Acids
• Polymers
• Made of nucleotides
– 5-Carbon Sugar
– Phosphate Group
– Nitrogen Base
• The bases are the INFORMATIONAL part of DNA!!
DNA vs. RNA
DNA
RNA
• Usually double stranded
• Single stranded
(some viruses have single
– mRNA – carries instructions
for making proteins-transmits
stranded DNA)
genetic info
• Stores Genetic Info
– tRNA – transfers AA
• 2 strands held together by
– rRNA – assembles AA
weak H bonds
• URACIL
• THYMINE
• Ribose sugar
• Deoxyribose sugar
BOTH are nucleic acids
BOTH are built from nucleotides
BOTH have A, C, and G
Replication Facts
• DNA has to be replicated
(copied) before a cell divides
• DNA is replicated during the
S phase (or synthesis phase)
of the cell cycle
• New cells will need identical
DNA strands
Enzymes involved with Dna replication
Helicase – unzips the DNA helix
Dna Polymerase- synthesizes the new DNA strands
by adding DNA nucleotides
Ligase- joins okazaki fragments
Protein Synthesis
• Anabolic
• Proteins are built of Amino Acids
• Genes code for proteins
– Transcription (RNA synthesis)
– Translation (assembling amino acids into proteins)
• Are all proteins the same size? Why or why not?
Genetic Code
• UNIVERSAL
– Although living creatures are diverse and unique
the components of their genetic code are the
same.
• Suggests a common ancestor
• Specific order of nitrogen bases (or
nucleotides) determines what proteins are
made, and therefore, what traits are
expressed.
Codon Chart = Universal
Gene Expression
• Gene expression is a regulated process
– Gene regulation results in a conservation of cell
resources
• Even though ALL of your cells have the same
genes, liver cells express different genes than
cardiac muscle cells, resulting in cell
differentiation
Lac Operon
• Inducible system
• Lactase is only produced in the presence of
lactose
• So if no lactose, no lactase produced…
• Gene regulation results in conservation of cell
resources
Genes code for proteins
• But not ALL of a gene is expressed
• Only EXONS code for proteins
• INTRONS are removed by RNA splicing
Mutations
• Heritable mutations occur in gametes
• Somatic mutations cannot be passed down
Types of Mutations – mistakes
a) Point Mutations – effects a single gene
i. Substitution
-Missense
-Nonsense
ii. Frameshift
-Insertion
-Deletion
b) Chromosomal mutations – most drastic,
change in structure or # of chromosomes (affects
many genes)many are due to non-disjunction.
Gene Mutations
The Effects of Point Mutations
► A point mutation is a change in a single base pair in DNA.
– A change in a single nitrogenous base can change the entire structure of a
protein because a change in a single amino acid can affect the shape of the
protein. (SUBSTITUTION)
mRNA
Normal
Protein
Stop
Replace G with A
Point
mutation
mRNA
Protein
Stop
Gene Mutations
Frameshift Mutations
► What would happen if a single base were lost from a DNA strand?
► A mutation in which a single base is added or deleted from DNA is
called a frameshift mutation because it shifts the reading of
codons by one base.
– As a result, every codon after the deleted base would be different.
Deletion of U
mRNA
Protein
• Mutations can be
– Good
– Bad
– Have no effect (silent)
•
•
•
•
Fixed by enzymes
Result in same AA
Occur in a non-coding region of DNA (such as an intron)
Occur in a gene that is not expressed(such as a
recessive trait)
Recombinant DNA and Biotechnology
• Biotechnology
• Genetic Engineering (Gene Therapy)
• Recombinant DNA-the genes of an organism are
changed by recombining its DNA with the DNA (or
genes) from another organism.
• Purpose- By inserting genes into the genome of an
organism, the scientist can induce the organism to
produce a protein it does not normally produce. This
can help improve the quality of life for that organism.
• Uses-bacteria that carry recombinant DNA can be
released into the environment to increase the fertility
of the soil, serve as an insecticide, or relieve pollution.
• How it works-Restriction enzymes catalyze
the opening of a DNA molecule at a
“restricted” point, regardless of the DNA's
source. Certain restriction enzymes leave
dangling ends of DNA molecules at the point
where the DNA is open. Foreign DNA can then
be combined with the carrier DNA at this
point. An enzyme called DNA ligase is used to
form a permanent link between the dangling
ends of the DNA molecules at the point of
union (Figure 1).
Genetic Engineering
The production of a recombined bacterium using a gene from a foreign donor and the synthesis of
protein encoded by the recombinant DNA molecule.
Techniques used to study genomes:
• Genetic modification – involves scientists identifying
and isolating genes that code for specific traits, and
then manipulating those factors that affect the genes’
expression.
– “GMOs” (genetically modified organisms) may have the
genes of another organism inserted to add a desired trait.
(For example, insect resistant GM cotton uses a gene from
a naturally occurring soil bacterium to provide it with builtin insect protection.)
– Gene therapy is a form of genetic modification used to
treat patients with genetic disorders. In theory, a patient
with a defective gene could have it replaced with a
working version of the gene.
Techniques used to study genomes:
•
DNA fingerprinting- is a process in
which a small sample of human DNA is
cut with a restriction enzyme. The DNA
fragments are separated according to
size using gel electrophoresis and DNA
probes. This creates a series of bands
based on the size of the persons DNA
fragments. The banding pattern
created is unique, with the exception of
identical twins. Banding patterns
produced by two samples can be
compared to establish whether the
sources are related (paternity case) or
come from the same person (crime
scene.) DNA fingerprinting is also
valuable for identifying the genes that
cause genetic disorders.
Think “Who stole the Cheese?”
Chromosomal analysis- involves using karyotypes to identify
chromosomal mutations in which an individual has an extra
chromosome or is missing a chromosome. These types of
mutations are caused by nondisjunction during meiosis.
Karyotypes can be used to identify the possible location of a
gene or a genetic abnormality on a chromosome.